JPS6211768A - Room temperature-curable silicone rubber composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition of high oil resistance, thus suitable for sealing materials for automobile FIPG use, by incorporating a known room temperature-curable silicone rubber composition with specified amount of an alkali metal salt of specific acid dissociation constant. CONSTITUTION:The objective composition can be obtained by incorporating (A) 100pts.wt. of a diorganopolysiloxane with the molecular end hindered by hydroxyl group of formula (R<1> and R<2> are each alkyl, cyclo alkyl, etc.; n>=5) with (B) 1-25pts.wt. of either organosilane or siloxane carrying in one molecule at least two hydrolyzable groups (e.g. methoxy, ethoxy) bonded to silicon atom (e.g., methyl trimethoxysilane) and (C) 0.1-50 (pref. 0.5-10)pts.wt. of a weak acid alkali metal salt with an acid dissociation constant pka 2-12 (e.g., potassium acetate).

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a curable silicone rubber composition, special C2, which has excellent oil resistance and is useful as a reel for automotive FIPG. (Conventional Provisional Technique) Seals around automobile engines have traditionally been oil-resistant and made from cork, organic rubber, asbestos, etc. gaskets and backing materials are used, but these have the disadvantages of being expensive, requiring complicated inventory management and process control, and having concerns about their sealing performance. Keyaki uses the FIPG method (Formed), which uses room temperature curable silicone rubber.
In PlaceGaskθts) is adopted.
:Although it has been highly evaluated in terms of workability, sealability, and heat resistance.

In recent years, gear oil used in automobiles such as transmissions has been increasing the amount of extreme pressure additives in order to improve fuel efficiency.
Molded products made from this organosiloxane have been considered to be low-viscosity, multi-grade products containing two or more organic siloxanes, so molded products made from this organosiloxane also suffer from deterioration and oil leakage during long-term use at high temperatures. .

Therefore, the room-temperature-curing silicone rubber used for this purpose (and as a countermeasure, a method of combining reinforcing silica and magnesium oxide with a specific surface area of 50 g/g or more (see Japanese Patent Application Laid-open No. 76055/1989) ], and a method of adding zinc carbonate or zinc oxide (Japanese Patent Laid-Open No. 59-804)
However, in recent years, the automobile industry has been using high-performance gear oils containing more extreme pressure additives, and higher temperature C:
Since durability of G sealing materials is required, such measures result in unsatisfactory performance.

(Structure of the Invention) The present invention relates to a room-temperature curable silicone rubber composition with excellent oil resistance that can solve these disadvantages, and which includes: 1) both ends of the molecular chain are blocked with hydroxyl groups; Diolkanopolysilokitis 100 moieties, 2) Organosilane or polyrokinane containing 2 or more hydrolyzable groups bonded to di-silicon atoms 1 to 25 moieties in one molecule, 3) Acid dissociation It is characterized by comprising 0.1 to 50 parts of an alkali metal salt of a weak acid having a constant pKa of 2.0 to 12.0.

That is, the present inventors have conducted various studies on ways to improve the gear oil resistance of room temperature curable silicone rubber compositions used as F'lPG sealants for automobiles. When an alkali metal salt of a weak acid with an acid dissociation constant pea of 2.0 to 12.0 is added to a rubber composition, the oil resistance of the rubber composition can be improved, especially when a large number of extreme pressure additives are added to the gear oil. They discovered that it is possible to obtain a room-temperature-curable silicone rubber with a high level of properties, and completed research on the type and addition of alkali metals to this weak acid, thereby completing the present invention.

The above-mentioned first and second components constituting the m-acid of the present invention are known as room temperature curable silicone rubber compositions, which are composed of hydroxyl groups in the first component and hydrolyzable in the second component. It becomes a rubber-like elastic body by condensation with a group.

The first component is dihydroxydiorgano, which is a diorganosiloxane in which both terminal groups are blocked with hydroxyl groups.

In this formula, R1 and R* are alkyl groups such as methyl, ethyl, and propyl groups, and groups substituted with halogen atoms, such as cyclohexyl groups.
'' may be the same group or a base group, and n in this formula represents a viscosity of the diorganopolysiloxane at 25°C of 25 to 500.000 oS (D range, preferably L<
is in the range of 1,000 to 100.000o8, so it is an integer of 5 or more.

Furthermore, the organosilane or silochitin as the second component constituting the composition of the present invention must have at least two hydrolyzable groups bonded to the middle silicon atom in one molecule.

This is because the hydrolyzable group easily causes a condensation reaction with the hydroxyl group in the first component, which acts to harden the composition. Decomposable groups include alkoxy groups such as methoxy, ethoxy, propoxy, isopropoxy and butoxy groups, organoketoxime groups such as acetoxime and butanone oxime groups, dimethylamino groups,
Organoamino groups such as diethylamino group and cyclohexylamino group, organoamide groups such as N-methylacetamide group, diorganoaminoxy group such as dimethylaminoxy group and diethylaminoxy group, alkenyloxy group such as propenyloxy group, etc. For example, this may be the same or different types as long as there are 22 or more in one molecule, and it may also be organosilane or organopolysilochitin. Examples include alkoxy compounds such as methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, ethyl orthosilicate, propyl orthosilicate, and enoxy compounds such as methyltripropenoxysilane and vinyltriisopropenoxysilane. based compounds, methyltris (acetone oxime) silane, methyl tris (butanone oxime)
Oxime compounds such as silane, methyltris(dimethylamino)silane, methyltris(diethylamino)
Amide compounds such as silane, methyltris(N-methylacetamido)silane, vinyltris(N-ethylacetamido)silane, etc.

Examples include aminoxy compounds such as methyltris(dimethylaminoxy)silane and methyltris(diethylaminoxy)silane, and these organosiloxanes can be prepared by partially condensing the above-mentioned silanes or by combining them with other siloxitin units. Examples include low-polymerized siloxitin compounds having a linear, branched, or cyclic siloxane skeleton and the above-mentioned functional groups.

However, if the amount of organosilane or silochitin added is too small, the crosslinking of the composition of the present invention will be insufficient, and if the amount added is too large, the molded product obtained by curing this composition will become too hard. In this case, the room temperature curing rate is 100 parts by weight (2 parts by 0 parts by weight).
The range is preferably 5 to 30 parts.

Next, the alkali metal salt of a weak acid as the third component constituting the composition of the present invention acts as an oil resistance improver for the silicone rubber molded product obtained by curing this composition. This is because the extreme pressure additive in gear oil generates an acid component when heated, which coats the iron surface and prevents the gear from seizing, but this acid component also causes deterioration of silicone rubber. Therefore, if this is neutralized with a weak acid alkali metal salt, the gear oil resistance of silicone rubber will be improved. Accordingly, this will improve the oil resistance of silicone rubber, especially against gear oil containing a large amount of extreme pressure additives. However, it has been confirmed through experiments by the present inventors that these do not exhibit such an effect when their acid dissociation constant is less than 2.0 or exceeds 12.0. It is necessary that the acid dissociation constant pK& is in the range of 2.0 to 12.0. Examples of alkali metal salts of weak acids with a pKa of 2.0 to 12.0 include potassium acetate (4,7), sodium propionate (4,9), sodium acrylate (4,3), and sodium methacrylate (4,3). , 33 and carboxylate salts such as sodium benzoate (4, 23), potassium carbonate (6, 4), sodium phosphate (2,
Inorganic acid salts such as 1) are exemplified [the above values indicate pKa values], but the amount added is 0 to 100 parts by weight of diorganopolysiloxane as the above-mentioned '@1 component.
．． If it is less than 1 part by weight, the object of the present invention to obtain a silicone rubber molded product with good oil resistance will not be achieved, and if it is more than 50 parts by weight, the rubber physical properties of the cured product obtained from the composition of the present invention will be poor. Therefore, it is necessary to set it in the range of 0.1 to 50 parts, but this preferable range is 0.5 to 1
0 parts by weight.

The composition of the present invention is obtained as a one-component room temperature curable composition by uniformly mixing predetermined amounts of the first to third components in a dry atmosphere. and 9
A two-component product may be used in which the homogeneous mixture of the third component and the second component are packaged separately and mixed together at the time of use. Also,
When this composition is exposed to air, a crosslinking reaction proceeds due to the moisture in the air, resulting in a rubber-like elastomer. Compounds, quaternary ammonium salts, organometallic compounds, titanium chelate compounds, guanidyl group-containing compounds, etc. may be added, and inorganic fillers for adjusting the physical properties of the desired rubber-like elastic body, For example, fumed silica, precipitated silica as a known powdered ice filler,
Hydrophobic treated silica, magnesium oxide, zinc carbonate, basic zinc carbonate, zinc oxide, carbon black, titanium dioxide, ferric oxide, aluminum oxide, calcium carbonate.

Quartz powder, (sodium earth, calcium silicate, talc,
Asbestos, glass fibers, organic fibers, etc. as fibrous fillers may be added to bentonite and dryness within a range that does not impair the object of the present invention.

In addition, a coloring agent, a heat or cold resistance improver, a thixotropic agent, a dehydrating agent, an adhesion aid, etc. may be added to the composition I of the present invention. Just add it.

In short, the composition of the present invention has an acid dissociation constant pKa of 2.0 to 12.
The addition of an alkali metal salt of a weak acid of 0.0% improves its oil resistance, and this is due to its properties and practicality, as all of its components are relatively easily available. It is considered to have a high

This composition is used as a FIPG material in the automobile industry due to its oil resistance and sealing properties, as well as in tillers, tillers, etc.
In addition to being useful as a sealing material around the engine, around the transmission, around the differential gear, etc. of various construction machines, it is also used in areas where oil resistance is required in equipment for the construction industry, electrical industry, and electronic industry. It can also be advantageously used as a sealing material.

Next, two examples of the present invention will be given. All parts in the examples are parts by weight, and the viscosity is a value measured at 25°C.

Example 1 Both ends of the molecular chain are blocked with hydroxyl groups, viscosity is 5.200
8 parts of methyltri(methylethylketoxime)silane, 17 parts of magnesium oxide having an average particle size of ao pm, 15 parts of fumed silica, and 0.2 parts of dibutyldenedioctate were added to 100 parts of dimethylpolysiloxane (C8) in an anhydrous state. Samples 1 to 2 were prepared by adding 2.5 parts of the alkali metal salts of weak acids shown in Table 1.

Next, sheets with a thickness of 2 thick were made from these samples ■～■, and they were made into rubber-like elastic bodies by electrical discharge at 23℃ for about 55 days.・After soaking in Castle Gear Oil 80W-90 (trade name manufactured by Yotameko Co., Ltd.) for 10 days, physical properties were measured using the JIS-6301 method.
The results shown in @L table were obtained.

Example 2 Both ends of the molecular chain are blocked with hydroxyl groups, viscosity is 19.60
100 parts of dimethylpolysiloxane of 0o8, 6 parts of vinyl tri(impunopenoki ν) silane, average particle size 30μ
90 parts of zinc carbonate powder, 7.5 parts of carbon black
1 part and 0.5 part of the guanidyl group-containing compound of the formula were mixed in an anhydrous state to prepare sample 1 [V].
l! Sample X-■ was prepared by adding the amounts of potassium methacrylate shown in Table C2.

Next, sheets with a thickness of 2 m were made from these samples ■ to ■ and treated in the same manner as in Example 1 to obtain a rubber-like elastic body. Castle gear oil 80W~90 (
Part I of above): When the physical properties of the rubber were examined after immersion for 10 days, the results shown in Table 2 were obtained.

Implementation @3 Both ends of the molecular chain are blocked with hydroxyl groups, viscosity is 5.100
100 parts of dimethylpolysilochitin (2, 8 parts of vinyltri(methylethyl-reketoxysilane), 90 parts of chlorinated zinc carbonate powder with an average particle size of 20 μm, 10 parts of fumed silica, r-aminopropyltrimethoxy) Sample XI was prepared by uniformly mixing 1.0 part of silane, 0.2 part of dibutyl ink octoate, and 2.5 parts of potassium methacrylate in an anhydrous state.

Next C: A sheet with a thickness of 'p2ti+ is made from this sample XI and treated in the same manner as in Example 1 to form a rubber-like elastic body.
This is heated to 120℃: the IF that was maintained! ll car gear oil fist castle MO gear oil special 75W-90
() Yota Jiko Co., Ltd. product name) and Castle Gear Oil 80, an automotive gear oil with more extreme pressure additives than this.
When the physical properties of the rubber were examined after being immersed in W-90 (mentioned above) for 10 days and 20 days, the results shown in Table @3 were obtained.

In addition, regarding this rubber-like elastic sheet C, please attach it to the upper surface of one end of the JIS G-3141 cold rolled iron plate 1 of 100mm x 25mxl, whose surface has been polished with sandpaper in advance. Seal material 2 is placed in an area of 25m x IOIm, and a thickness of 21m is placed between the coated surfaces.
After placing the Teflon plate of jI as spacer 3,
The same iron plate 1 as above is placed on top of this, and as shown in the figure (=
Place 4 weights of C2500.9 on this, and then attach these 2
The coated surface was left to harden for 96 hours in an atmosphere of 3°C and 55% RH, and the shear adhesive strength was measured after immersing it in the two types of gear oils mentioned above. It was as listed in Table C2.

[Brief explanation of the drawing]

FIG. 1 shows a perspective view of a method for measuring the shear adhesive strength of the composition of the present invention. 1... Adhering iron plate, 2... Seal material, 3... Spacer, 4... Weight.

Claims (1)

[Scope of Claims] 1.1) 100 parts by weight of diorganopolysiloxane whose molecular chain ends are capped with hydroxyl groups, 2) Contains two or more hydrolyzable groups bonded to silicon atoms in one molecule. 3) 0.1 to 50 parts by weight of an alkali metal salt of a weak acid having an acid dissociation constant pKa of 2.0 to 12.0. silicone rubber composition.